1. Field of the Invention
The present invention relates to an information processing apparatus, communication method, and storage medium, which transfer and process data using a ring-shaped bus.
2. Description of the Related Art
As a conventional method of efficiently transferring packets in a data-path control system in which a plurality of modules are connected to be able to communicate with each other, and execute parallel processes, a method of transferring packets according to their priority levels has been proposed.
Japanese Patent Laid-Open No. 11-167560 describes the following data transfer method. That is, in this data transfer method, a plurality of modules each including one or more stages of buffers or memories are connected in a ring shape, and packets as many as the number of modules are transferred on a ring bus, thus parallelly transferring the packets between modules and executing data processes. In the arrangement of Japanese Patent Laid-Open No. 11-167560, priority levels are determined by central control, thus implementing transfer according to the priority levels.
Japanese Patent Laid-Open No. 2007-316699 describes a packet transfer method based on priority levels distributed to respective modules. More specifically, modules are connected via two ring-shaped buses, that is, a data transfer bus and response transfer bus. Then, each module compares priority levels between a packet transferred from another module via the ring bus, and a packet generated by that module. When the generated packet has a higher priority level, the module discards the transferred packet. Then, the module outputs the packet generated by itself onto the ring bus. The module notifies, using the response transfer bus, a module as a transmission source of the transferred packet that the transferred packet is discarded. The module which is notified that the packet is discarded re-transmits the discarded packet. Then, packets are transferred based on priority levels.
When data transfer according to priority levels is implemented by central control as in the method of Japanese Patent Laid-Open No. 11-167560, a control circuit is more complicated as the number of modules increases, resulting in an increase in circuit scale. With the method of Japanese Patent Laid-Open No. 2007-316699, all the modules have to copy and hold all transmitted packets by the self modules until it can be judged that the transmitted packet is not discarded by another module. For this reason, a buffer size used to hold copies of transmitted packets increases considerably in proportion to an increase in the number of modules.
By contrast, Japanese Patent Laid-Open No. 2010-217959 describes a method which connects respective modules via a ring bus, and controls each module to transfer a data packet processed by that module to the next module, thereby executing a series of processes. With the arrangement of Japanese Patent Laid-Open No. 2010-217959, after a process is complete in a certain module, a signal including an identifier used to identify that module is output onto the ring bus. A module which executes the next process stores, in advance, an identifier of a module which executes an immediately preceding process, and executes a process if the signal includes that identifier. Also, in Japanese Patent Laid-Open No. 2010-217959, when a module suspends a process, it transfers a signal including information indicating that the process is suspended. When a module receives a signal, which was transmitted by itself and includes information indicating that a downstream module suspended a process, the former module determines that a module which executes a process immediately after the self module cannot process any more information transmitted from the self module, and pauses information transmission. Thus, in distributed control, efficient packet transfer is implemented by a small storage capacity.
In the method of Japanese Patent Laid-Open No. 2010-217959, a certain module detects whether or not suspension has occurred in a module which executes a process immediately after the self module. For this reason, when a module which executes a further downstream process suspended the process, modules which execute upstream processes may unwantedly continue processes. As a result, the number of suspended packets increases, resulting in a deadlock.
The present invention has been made in consideration of the aforementioned problems, and provides an information processing apparatus, information processing method, and storage medium, which execute appropriate transmission interval control based on a processing state of a processing device connected to each of communication devices, which are connected via a ring bus.